This HMM represents the G subunit (one of 14: A->N) of the NADH-quinone oxidoreductase complex I which generally couples NADH and ubiquinone oxidation/reduction in bacteria and mammalian mitochondria while translocating protons, but may act on NADPH and/or plastoquinone in cyanobacteria and plant chloroplasts. This HMM excludes related subunits from formate dehydrogenase complexes.